As another Ex-GDR citizen here, I think the most subversive were the thick shopping catalogs of the big West-German mail-order companies (Otto, Quelle, Conrad [Electronics]).
I don't remember how or why we got them, but for some reason we did, once in a while. I think they should have been confiscated at the border, but apparently enough West German visitors happened to have one with them on visits, that remained undiscovered, or they were left in some of the many parcels (especially around Christmas time) sent from West to East Germany.
We would look through those thick foto-color glossy paper catalogs, looking at one unobtainable item after another. In every category, from clothes, furniture, tools, toys, to electronics. The difference in quality was several decades, the difference in variety and quantity was at least two orders of magnitude, with many items having no equivalent at all in the East.
The paper and the print quality alone were on another level, and they made that for a throwaway shopping catalog?
Just for comparison, when I turned 14 and was given some money I spent about 1100 East German Marks on a mono cassette recorder (https://ddr-hifi-technik.de/wp-content/uploads/2023/03/IMG_2...). At the same time a stereo recorder's price in West Germany was something like 99 DM. I could not afford the East German stereo variant, that would have cost 1400 East German marks. A typical salary in East Germany was around 1000 East German Marks.